Field of the Invention
The present invention relates to an extruded honeycomb body of a ceramic or metallic material with a multiplicity of conduits being separated from each other by partitions and extending approximately parallel to each other. Such honeycomb bodies, which are used in catalytic converters of internal combustion engines in particular, have been described in U.S. Pat. No. 3,853,485, for example.
Such bodies are usually extruded from a powdery or granulate-like ceramic material, dried and subsequently baked.
Of late, that method of production has also been employed for producing electrically conductive honeycomb bodies which can be electrically heated, wherein a metallic material or a mixture of ceramic and metallic materials is used. Such honeycomb bodies have been described, for example, in European Patent Application 0 465 184 A1. In order to affect the electrical resistance and the course of an electric current in such a honeycomb body, slits are additionally provided which generally extend parallel to the extruded structures.
Either squares, rectangles or other polygons are typical cross-sectional shapes of conduits in extruded honeycomb bodies. Various polygonal progressions have been described as cross-sectional shapes in particular in U.S. Pat. No. 3,853,485, in which varied numbers of conduits per cross-sectional surface are provided in the various cross-sectional regions.
However, it is common for all heretofore-known extruded honeycomb bodies to have preferred orientations of the conduit or channel walls, wherein the preferred orientation of the conduit walls leads to reduced elasticity in the direction of the preferred orientation. With square conduits, the bodies have practically no elasticity in the direction of the webs, and elasticity is also very low in typical hexagonal honeycomb shapes. That does not even change if additional walls are disposed in various directions, as is disclosed in U.S. Pat. No. 3,853,485.
Besides the extruded honeycomb bodies which have been known for many years, honeycomb bodies made of sheet metal are employed in increasing numbers, wherein suitable honeycomb bodies are produced by suitable structuring and disposition of the sheet metal in layers. Besides the initially used honeycomb bodies wound spirally or helically from sheet metal, a plurality of shapes with considerably increased elasticity have become known in the meantime. In that connection a principal structure which is very important for elasticity has been described in European Patent 0 245 736 B1, in which the individual sheet metal layers extend in an approximately involute shape from a center outward. Honeycomb bodies produced in accordance with that principle have also been described in International Patent Application WO 90/03220, corresponding to U.S. Pat. Nos. 5,105,539; 5,135,794; and 5,139,844, and, in a somewhat changed shape, also in International Patent Application WO 92/02717, corresponding to U.S. application Ser. No. 08/016,041, filed Feb. 10, 1993. Similar properties also result in connection with bodies being formed of sheet metal wound in an S-shape, wherein the elastic properties and the oscillating behavior can be affected by additional reinforced layers, such as is described in International Patent Application Wo 89/07488, corresponding to U.S. Pat. No. 5,102,743. Those and similar structures have been shown to be particularly suited for electrically heatable honeycomb bodies, especially because of their elasticity, such as is recited in International Patent Application WO 92/02714, corresponding to U.S. Pat. No. 5,411,711.